Walking Dead fans, listen up! AMC just released a video that includes some majorly intriguing news about season 4. Okay, so you know how the cast and crew has been working overtime to promote the "unreal" new threat that's going to be unveiled this season? For months now they've been talking about how the zombies are going to blow our damn minds, with actor Norman Reedus going so far as to tease, "They’ve introduced a way to make zombies scary again, and they’re terrifying. The new threat is just unreal."

My theory at the time was that we'd be seeing herds -- enormous, crazy-dangerous groups of walkers -- but based on one sentence from Lauren Cohan (Maggie) in AMC's new "Greetings from the Set" video, the most deadly threat of all to the survivors in season 4 isn't coming from walkers … OR outside people.

(Stop reading now if you want to avoid potential spoilers and speculation!)

Let's start with the other details teased in this new video. In a nutshell, here's the latest scoop about what we'll see in the first episodes:

• There are more zombies than ever before.• They're more decayed, and thus even creepier.• Another winter has passed in Walking Dead-ville.• They've worked hard to make the prison feel like a home, and things have evolved quite a bit since we last saw it.• Rick's got himself a dang old farm, y'all.• Things haven't exactly been comfortable, but they've had a system for a while that's kept them fairly safe. (The premiere episode, notably, is titled "30 Days Without an Accident.")

Oh, and also? According to Lauren Cohan,

It's not even the walkers and it's not even other people this time, there's a whole new threat.

Creator Robert Kirkman adds,

That could be more deadly than the other two combined.

Here's the clip, which is definitely worth watching:

So the great big new threat … ISN'T zombies? Or it is, but not directly? Here's what David Morrisey told i09 a while back:

There's a whole new threat in this season that we have to deal with which you get to know about. (…) This new threat is the thing that overall is the thing for us. The zombies are the same threat that they've always been, but with this added extra that makes the world a very, very dangerous place. And people start to sort of react in different ways ... It's not a threat you're going to be able to kill very easily. So it's something that happens within the world. Another thing. And that is very dangerous. It's very dangerous and I think when you see it, you'll ... there's a lot of identity with it, for us in our world. You'll get it when you see it. Each person reacts to it very differently.

Also, there's this from Robert Kirkman at Comic-Con:

Things are definitely going to be way crazier and getting worse. People are more ragged, more terrible things are happening and people are having to deal with it.

Okay then! Here are my two theories about what this all means:

1) There's a psycho within the prison that's sabotaging the group's safety. He or she is feeding walkers and luring them in so that people are getting killed despite all the new safety measures in place, and this person is also directly attacking survivors (as hinted at in the season 4 trailer, which seems to reference an inside job attack at the prison that leaves 12 people dead, 2 murdered in "cold blood" and the other 10 presumably by walkers).

2) Survivors start turning to suicide in a rash of hopelessness after some awful incident that compromises their prison, which they've come to view as a home.

I'm leaning towards option #1, but I'm thrown off by Cohan's specific wording: "It's not even other people this time." Does she mean it's not outside people, like the Governor? Or does she mean the super-deadly threat isn't coming from people in general?

At any rate, something happens that messes with Tyreese in a big way, based on what we saw in the trailer. First he looks like this:

Then later he's robotically fighting zombies in a scene as if he's totally emotionally traumatized. My guess is that he got a close-up glimpse of a very dead Sasha, but as for how she may have succumbed (by a homicidal lunatic prone to decapitation, similar to the comics? Or a grotesque double suicide, also similar to the comics? Or by a hungry walker? Or …?), I guess we're just going to have to wait to find out.